Exit polls of voters in Pennsylvania's Democratic presidential primary show that working-class, white voters are sticking with Hillary Rodham Clinton.

They have been at the core of her support in most states so far. In Pennsylvania, about two-thirds of whites without college degrees were backing her -- as were about the same number of whites from families earning under $50,000 a year.

Clinton won among blue-collar voters, women and white men. Obama was favored by blacks, the affluent and voters who recently switched to the Democratic Party, a group that comprised about one in ten voters, according to the survey conducted by The Associated Press and the TV networks.

Obama was running ahead in Philadelphia and the populous surrounding suburbs, while Clinton was leading in Pittsburgh and the western part of the state as well as the blue-collar area around Scranton, the same polls showed.

Both rivals sought to shape expectations in advance.

Trailing in the national delegate chase and outspent badly in the state, Clinton needed a win to sustain her candidacy. She projected confidence by scheduling a rally in Philadelphia after the polls closed.

Obama, the front-runner, said he expected to lose, but narrowly, and worked to limit any erosion in his delegate lead. Even before the polls closed, he flew off to an evening rally in Indiana, one of two states with primaries on May 6.